1. Field of the Invention
The present invention relates to an optical interferometer to be used in the field of, for example, metrology.
2. Description of the Related Art
FIG. 6 is a plan view schematically showing an example configuration of a conventional optical interferometer. In the drawing, reference numeral 1 designates incident light; 2 designates a beam splitter; 3 and 4 designate mirrors; and 5 designates a photodetector.
As shown in the drawing, by means of a beam splitter 2, the incident light 1 is divided into two optical paths which are orthogonal to each other; that is, transmitted light and reflected light. Light reflected by the mirror 3 provided in and oriented at right angles to the optical path for the reflected light and light reflected by a mirror 4 provided in and oriented at right angles to the optical path for the transmitted light are again merged into a single ray by means the beam splitter 2.
At this time, the mirror 3 is moved along the optical path at constant velocity by means of an unillustrated stage on which the mirror 3 is mounted. Consequently, a difference in length arises between the optical path over which the light reflected by the mirror 3 travels and the optical path over which the light reflected by the mirror 4 travels, thus resulting in a variation in the intensity of interference fringes.
The photodetector 5 extracts, as an electric signal, such a variation in the intensity of interference fringes.
As mentioned above, in the above-described conventional optical interferometer, the mirror 3 is moved along its optical path over a long distance, thus resulting in time-consuming operation. Moreover, the accuracy of the optical interferometer must increases with the distance over which the mirror is to travel.
For these reasons, a limitation is imposed on a reduction in the size of and the measurement time required by the conventional optical interferometer. Further, there is also desired an improvement in the optical interferometer in terms of accuracy management.
Accordingly, an object of the present invention is to provide an optical interferometer of reduced measurement time, and improve measurement accuracy, and facilitated accuracy management.
Another object of the present invention is to provide a compact optical interferometer.
To these ends, according to a first aspect of the present invention, there is provided an optical interferometer, wherein incident light is divided by means of a beam splitter into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, the interferometer comprising:
a third reflector which reflects the incident light at right angles so as to fall on the beam splitter;
a fourth reflector which reflects the light, having been transmitted through the beam splitter, at right angles so as to fall on the second reflector; and
a moving member on which the beam splitter and the third and fourth reflector are mounted and which can be moved along an optical path extending between the first reflector and the photodetector.
The reflector is typified by a mirror. However, a corner cube or a reflector may be used in place of the mirror.
The photodetector extracts, as an electric signal, a variation in the intensity of interference fringes.
The moving member is usually called a stage.
To these ends, according to a first aspect of the present invention, there is provided an optical interferometer, wherein incident light is divided by means of a beam splitter into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, wherein a moving member on which the beam splitter and the third and fourth reflector are mounted is moved along an optical path extending between the first reflector and the photodetector. Consequently, the optical path over which the light reflected by the first reflector travels and the optical path over which the light reflected by the second reflector travels can be changed simultaneously. Thus, the optical interferometer of the present invention can achieve the same optical path difference as that achieved by the conventional optical interferometer, by employment of a travel distance which is one-half that required by the conventional optical interferometer.
Since the optical interferometer of the present invention requires one-half the travel distance required by the conventional optical interferometer, measurement time can be shortened.
Further, since a required travel distance is short, blurring stemming from movement of the moving member can be diminished. Therefore, there can be realized facilitation of accuracy management of parts, an improvement in measurement accuracy, and miniaturization of the optical interferometer.
Preferably, the optical interferometer further comprises:
a fifth reflector which reflects the light reflected by the beam splitter in a direction parallel to the path of the light reflected by the beam splitter (hereinafter called xe2x80x9cin a parallel directionxe2x80x9d) so as to fall on the first reflector; and
a sixth reflector which reflects the light reflected by the fourth reflector in a parallel direction so as to fall on the second reflector, wherein the first and second reflectors are mounted on the moving member.
As mentioned above, the light reflected by the beam splitter is reflected in a parallel direction by means of the fifth reflector so as to fall on the first reflector. Further, the light reflected by the fourth reflector is reflected in a parallel direction by means of the sixth reflector so as to fall on the second reflector. The first and second reflectors are mounted on the moving member on which the beam splitter and the third and fourth reflectors are mounted. Hence, the travel distance can be shortened to one-half that required by the previously-described optical interferometer of the present invention. Accordingly, the travel distance required by the optical interferometer of the present invention can be shortened to one-fourth that required by the conventional optical interferometer.
According to a second aspect of the present invention, there is provided an optical interferometer, wherein incident light is divided by means of a beam splitter into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, the interferometer comprising:
a third reflector which reflects the light, having transmitted through the beam splitter, at right angles so as to fall on the second reflector; and
moving means which synchronously moves the first and second reflectors inn opposite directions so as to approach or depart from each other, along an optical path extending between the first reflector and the photodetector.
As mentioned above, incident light is divided by means of a beam splitter into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, wherein moving means synchronously moves the first and second reflectors in opposite directions so as to approach or depart from each other, along an optical path extending between the first reflector and the photodetector. Thus, the optical path over which the light reflected by the first reflector travels and the optical path over which the light reflected by the second reflector travels can be changed simultaneously. Since the first reflector and the second reflector can be moved simultaneously in opposite directions, the optical interferometer of the present aspect of the invention can perform measurement within one-half the time required by the conventional optical interferometer.
Since the distance over which each of the first and second reflectors are to move is shortened to one-half that required by the conventional optical interferometer, blurring stemming from movement of reflectors can be diminished, thus facilitating accuracy management of parts and improving measurement accuracy.
Preferably, the moving means comprises a feed screw member having helical threads of opposite hands (hereinafter called xe2x80x9copposite-hand helical threadsxe2x80x9d), and the feed screw member is disposed in parallel to the optical path extending between the first reflector and the photodetector, the helical thread of one hand being engaged with the moving member having the first reflector mounted thereon and the helical thread of the other hand being engaged with the moving member having the second reflector mounted thereon.
As mentioned previously, a feed screw member is disposed in parallel with the optical path extending between the first reflector and the photodetector and has opposite-hand helical threads. The helical thread of one hand is engaged with a moving member having the first reflector mounted thereon, and the helical thread of the other hand is engaged with another moving member having a second reflector mounted thereon. In addition to yielding the advantageous result yielded by the optical interferometer of the second embodiment, the optical interferometer of the third embodiment yields the advantage of simultaneous movement of the first and second reflectors in opposite directions by means of rotation of the feed screw member.
According to a third aspect of the present invention, there is provided an optical interferometer, wherein incident light is divided by means of a beam splitter into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, the interferometer comprising:
a third reflector which reflects the light, having transmitted through the beam splitter, at right angles so as to fall on the second reflector; and
a moving means on which the first and second reflectors are mounted and which can be moved along the optical path extending between the first reflector and the photodetector.
As mentioned above, by means of a beam splitter, incident light is divided into reflected light and transmitted light which travel along respective optical paths, which are orthogonal to each other; the reflected light is subjected to total reflection by a first reflector and the transmitted light is subjected to total reflection by a second reflector; and the reflected light rays are again merged by the beam splitter into a single ray so as to fall on a photodetector, wherein moving means on which the first and second reflectors are mounted is moved along the optical path extending between the first reflector and the photodetector. As a result of simultaneous movement of the first and second reflectors in a single direction, the optical path over which the light reflected by the first reflector travels and the optical path over which the light reflected by the second reflector travels can be changed simultaneously. Consequently, the optical interferometer of the present invention can achieve the same optical path difference as that achieved by the conventional optical interferometer, within a travel distance which is one-half that required by the conventional optical interferometer.
Thus, since the optical interferometer of the present invention requires one-half the travel distance required by the conventional optical interferometer, measurement time can be shortened.
Further, since the travel distance required is short, blurring stemming from movement of the moving member can be diminished. Therefore, there can be realized facilitated accuracy management of parts and an improvement in measurement accuracy.
Preferably, the optical interferometer further comprises a fourth reflector which reflects the incident light at right angles so as to fall on the beam splitter;
a fifth reflector which reflects the light reflected from the beam splitter in a parallel direction so as to fall on the first reflector;
a sixth reflector which reflects the light reflected from the third reflector in a parallel direction so as to fall on the second reflector; and
a second moving member on which the fifth and sixth reflectors are mounted and which can be moved along an optical path extending between the fifth reflector and the photodetector, wherein
the beam splitter and the third and fourth reflectors are mounted on the first moving member having the first and second reflectors mounted thereon.
Incident light is reflected at right angles by means of the fourth reflector so as to enter the beam splitter, and the light reflected by the beam splitter is reflected in a parallel direction by a fifth reflector so as to fall on the first reflector. The light, which has been transmitted through the beam splitter, is reflected at right angles by the third reflector. The thus-reflected light is further reflected in a parallel direction by a sixth reflector so as to fall on the second reflector. The third and fourth reflectors are mounted on a first moving member on which the first and second reflectors are mounted, and a second moving member having the fifth and sixth reflectors mounted thereon is moved along the optical path extending between the fifth reflector and the photodetector. In addition to the previously-described advantageous result, the optical interferometer of the present invention requires an advantage of further shortening a required travel distance; i.e., shortening of a travel distance to less than one-half the travel distance required by the conventional optical interferometer.